1. Field of the Invention
This invention pertains to coaxial cable jacks and more particularly to a coaxial cable jack module with inductive monitoring.
2. Prior Art
In the prior art, jack modules for coaxial cable connections are well known. An example of such is shown in commonly assigned U.S. Pat. No. 4,749,968 to Burroughs.
The Burroughs patent shows a jack module 20 which includes a configuration (utilizing the embodiment of FIG. 8 of the patent) having two parallel spaced apart central conductors connected by a switch mechanism. The switch mechanism electrically connects the two parallel spaced apart central conductors when a plug is absent from ports associated with the central conductors. Upon insertion of a plug into either of the ports associated with the two central conductors, the-switch isolates the other central conductor to ground.
As shown in the Burroughs patent, jacks of the type shown therein may be associated with single central conductor jacks for monitoring purposes. When a single jack is used in a monitoring configuration, the single jack is connected across either a resistance or inductance circuit to one of the central conductors which are joined by the switching mechanism. Insertion of a plug into the monitor jack permits monitoring of a signal flowing through the two parallel central conductors without disruption of the signal.
In the prior art, jack modules having a monitor central conductor joined in a common housing with two central conductors joined by a switch are known. An example of such is shown in U.S. Pat. No. 5,246,378, issued Sep. 21, 1993.
In the aforementioned U.S. Pat. No. 5,246,378, monitoring is provided across a resistive circuit. Namely, a monitor conductor is connected to a main signal conductor across an electrical resistor (commonly 100 ohms). A plug may be inserted into the housing to make electrical connection with the monitor conductor. Due to the resistive drop, a signal across the main conductor can be monitored without interruption of the signal.
In the aforementioned U.S. Pat. No. 5,348,491, reference is made to a monitor network which provides for inductive monitoring. Inductive monitoring is preferred in certain applications since it can result in a lower power loss through the network.
Unfortunately, an inductive monitoring circuit presents certain risks with respect to a jack module for use in telecommunications. Unlike a resistive monitoring circuit, an inductive monitoring circuit places an inductor in series with the main signal conductor. Accordingly, if an electrical connection between the inductor and the main signal conductor is broken, the signal across the main signal conductor is lost. In high bit rate transmissions, such a loss is undesirable since a substantial amount of a customer's communications or data would be lost. This risk is normally not associated with resistive monitors since the monitor circuit is connected in parallel across a resistance. As a result, if the connection of the resistor to the main signal conductor is broken, the main signal conductor itself is not broken and there is no signal loss.
In monitoring circuits using inductive monitoring, windings are provided around magnetic cores. The windings are very fragile conductors which typically may be connected to a printed circuit board by stamping the ends of the winding to flatten the ends prior to soldering onto a contact pad on a printed circuit board. This presents a higher risk of breakage since a small wire is used which is susceptible to thermal stresses, vibration and mechanical shock.
It is an object of the present invention to provide an inductive monitoring circuit which is less susceptible to signal interruption.